Machine for forming nonwoven webs



Dec. 2, 1969 J. E. OWENS ET AL 3,481,005

MACHINE FOR FORMING NONWOVEN WEBS Filed Nov. 21, 1967 2 Sheets-Sheet l-29 5 12 II? IIIIIIIIIIlilllllllfilillillllfz M/l/fmfis Dec. 2, 1969 J.E. QWENS ET AL 3,481,005

MACHINE FOR FORMING NONWOVEN WEBS Filed Nov. 21. 1967 2 Sheets-Sheet 2INVENTORS United States Patent MACHINE FOR FORMING NONWOVEN WEBS John E.Owens, Hockessin, and Dimitri P. Zafiroglu,

Wilmington, Del., assignors to E. I. du Pont de 'Nemours and Company,Wilmington, Del., :1 corporation of Delaware Filed Nov. 21, 1967, Ser.No. 684,792 Int. Cl. D01g 25/00, 27/00 U.S. Cl. 19--156.4 6 ClaimsABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field Thisinvention relates to an improved random fiber nonwoven Web formingmachine.

Description of the prior art The principle of forming random nonwovenwebs by dispersing loose textile fibers into an air stream andsubsequently condensing the fibers onto a foraminous surface to form abatt is well known. There are several commercial machines employing thisprinciple, some of which are described by F. M. Buresh at page 13-21 ofNonwoven Fabrics, Reinhold Publishing Corp, 1962. Of the commercialmachines, the most common is sold by the Curlator Corporation under thename Rando-Webber. Rando-Webbers are described in the patent literaturein the following patents: US. 2,451,915, issued Oct. 19, 1948; US.2,700,188, issued Jan. 25, 1955; US. 2,703,441, issued Mar. 8, 1955; US.2,744,294, issued May 8, 1956; and US. 2,890,497, issued June 16, 1959.

A problem with the presently known machines has been to maintain arandom distribution of the fibers in the air stream before the fibersare condensed. This problem is particularly aggravated when the fiberspick up nonuniform static electrical charges from triboelectric or othereffects. This problem usually manifests itself in the condensing Zone,Where the air velocity is lower than it is in the dispersing zone. Asthe air speed is lowered to permit the fibers to condense, tufting ofthe fibers occurs which seriously detracts from web uniformness andquality. Unless the fibers can be maintained in random distribution,capacity of the machines is severely lowered. In the past, this fiberdistribution problem in the air stream has been a limiting factor uponcapacity.

SUMMARY OF THE INVENTION According to this invention, there is provideda machine for forming random fiber Webs by dispersing the fibers in agaseous medium and subsequently condensing the fibers onto a foraminoussurface. This machine comprises, in combination:

(a) means for dispersing the fibers in the gaseous medium;

(b) means for supplying the gaseous medium;

(c) means for feeding the fibers to the dispersing means;

(d) means for condensing the fibers from the gaseous medium;

3,481,005 Patented Dec. 2, 1969 (e) a duct connecting the dispersingmeans to the condensing means, the duct containing the gaseous medium;and

(f) a corona discharge system located at a point beyond where the fibersare dispersed in the gaseous medium.

The corona discharge system comprises, in combination: (1) an ionemitting electrode; (2) a target electrode oppositely positioned acrossthe path of the fibers in the gaseous medium, the target electrode beingconnected to ground; (3) a source of electrical current and voltage; and(4) means connecting the ion emitting electrode to the source ofelectrical current and voltage.

A process is also provided for forming a random fiber nonwoven web. Thisprocess comprises:

(a) feeding fibers to a dispersing zone;

(b) dispersing said fibers into a gaseous medium at the dispersing zone;

(c) imparting a uniform electrical charge to said dis persed fibers inthe gaseous medium;

(d) conveying said dispersed fibers in the gaseous medium to acondensing zone; and

(e) condensing said dispersed fibers from the gaseous medium onto aforaminous surface in the condensing zone.

An advantage of the machine and process of this in vention is that animprovement in maintaining the ram dom distribution of dispersed fibersin the gaseous medium is realized due to the uniform electrical chargeon the fibers. Another advantage is that the fibers are maintained in anopen position, i.e.they are not doubled over, dur. ing conveyance fromthe dispersing zone to the condensv ing zone. These advantages permitnonwoven web form. ing machines to be run at higher capacities Whileproducing webs of a uniformness and quality which is comparable to thoseformed at lower capacities by prior art machines.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a cross-sectional view offiber dispersingfiber charging apparatus.

FIGURE 2 is a blown up cross-sectional view of the fiberdispersing-fiber charging system shown in FIGURE 1 which illustrates thecorona discharge system in greater detail.

FIGURE 3 is a cross-sectional view of single condenser apparatus.

FIGURE 4 is a cross-sectional view of a dual condenser apparatus.

FIGURE 5 is a front view of one of the corona discharge electrodes shownin FIGURE 2.

DESCRIPTION OF THE INVENTION The elements of an ordinary, commercial airlaydown nonwoven Web forming system are shown in the figures. FIG. 1illustrates a feed fiber stock 1 which can be of many forms, i.e.opened,raw, carded, loose, in batt form, etc., and which is fed through afeeding system of feeding device 2 which can vary in form, shape andsize, to a disperser or lickerin roll 3, which revolves at high speedsand breaks away small :fiber groups from the feed to throw them into agaseous medium 4. The disperser roll 3 is normally covered with cardclothing, usually of the garnett type and generally has protruding teeth10. Finally, the gaseous medium 4 which is commonly an air stream,carries the dispersed fibers 5 through a duct '8 to a condensation zone(illustrated in FIGURES 3 and 4) where the fibers are condensed onto aforaminous or perforated, vacuum backed moving surface 6.

In addition to having the elements of prior nonwoven web formingmachines, the machines of this invention have a corona discharge systemlocated at a point in the apparatus after the fibers have beendistributed by the disperser roll 3. The corona discharge system is madeup of: (1) an ion emitting electrode 7 commonly having one or moreneedle points 12, the ion emitting electrode being connected to a sourceof electrical current and voltage; and (2) a target electrode 9 which isconnected to ground. As has been pointed out, imparting a uniform chargeonto the fibers as they pass through the ion flow created by the coronadischarge system helps to maintain good fiber distribution in thegaseous medium and consequently reduces the tendency of fibers to formtufts before and during the time they are condensed.

FIGURE 2 is a blown up view of the corona discharge system shown inFIGURE 1. In this view, it can be seen that the ion emitting electrode 7is made up of a conductive base 11 and one or more conductiveneedleshaped points 12. These needle points allow a sufficient build upof current density at the needle tips to cause a corona discharge tooccur thereby setting up a fiow of ions 23 from the ion emittingelectrode 7 to the grounded target electrode 9.

The duct 8, which carries the charged fibers from the dispersing roll 3to the condensation zone, normally is expanded toward the condenser end,thus creating a venturi effect within the duct. Because of this, thegaseous medium 4 has a higher velocity, V near the point at which thefibers are dispersed or venturi throat than the gas velocity, V near thecondenser apparatus. The lower velocity V facilitates the condensationof fibers from the gaseous medium 4.

FIGURE 3 illustrates a single condenser apparatus which comprises theduct 8 which conveys the charged fibers 5 dispersed in a gaseous medium4 to a foraminous condenser roll 13. The gaseous medium 4 may passthrough the foraminous roll and is either recirculated through thesystem or expelled. Nonwoven web material 14 is collected from thecondenser roll 13, which is grounded to remove the charge from thefibers.

A desirable secondary effect obtained by uniformly charging the fiberscan be observed in the web material collected from the condenser roll13. When the corona discharge system is not in use, the collected webmaterial 14 is thicker and more non-uniform at its surface than with anoperating corona system. In FIGURE 3, web material produced without theuse of corona discharge has a thickness t In contrast, the chargedfibers form a much thinner web due to electrostatic pinning and a moreuniform web illustrated in FIGURE 3 as having a thickness t FIGURE 4illustrates another possible embodiment of a condenser system. A dualcondenser system is shown comprised of two foraminous grounded belts 15driven by a series of drive rolls 16. The belts are angled so that thecondensed fibers are conveyed in a converging pattern thereby formingchevrons from the fibers. A desirable secondary effect of uniformlycharging the fibers is evidenced in a dual condenser apparatus by thelength of the chevrons 20, which are formed from the fibers convergingfrom the sides at an angle to form a V shape. When the corona dischargesystem is not used, the chevrons 20 are much shorter than when thecorona discharge system is turned on due to the electrostatic pinningeffect. In general, longer chevrons in a dual condenser system such asthat illustrated in FIGURE 4 mean the nonwoven web produced will bestronger than a web produced where the chevrons are shorter. The webproduced with charging is also more uniform.

The increased strength and uniformity of webs produced according to thisinvention can be explained in terms of three effects produced byuniformly charging the fibers. First, the good initial distribution offibers is maintained. Secondly, the fibers are electrostatically pinnedto the condensing surface resulting in thinner webs (single condenser)or longer chevrons (dual condenser). Third- 1y, since the fibers areWell pinned on the condensing surface, they are not disturbed as the webis conveyed away from the condensing zone. The first and third effectsincrease the uniformity of webs while the second results in increasedweb strength.

The first reason for tuft formation is simple overcrowding. At 5 lbs. offibers/in. of width/hour, for example, there are approximately 250,000-1denier per filament (d.p.f.), 1 inch staple fibers per inch of machinewidth per second. For 1 /2 d.p.f., 1 /2 inch staple, this figure isstill over 100,000. With all these fibers flying about, it is verylikely that, unless they are somehow made to repel each other, they willentangle and group into fiber tufts. This tendency is, of course,increased by air turbulence and disturbances in the system.

The tuft forming tendency is also reinforced by electrostatic attractionof fibers for each other, especially under conditions of low relativehumidity in the atmosphere. The primary source of this attraction israndom triboelectric charges imparted to the system before or at thefeed point. Conditions met by the fiber, prior to being separated intosmall fiber groups and gas borne, are such as to impart nonuniformcharges, not only .of different intensity but also of different polarityfrom fiberto-fiber. When atmospheric humidity is high, the fiber maylose most or all of these charges to the disperser roll or the feeddevice prior to being gas borne, since under such conditions, itssurface conductivity is high.

Because of tufting, web quality has not been sufficient withcommercially available machines at high rates, i.e. 2-3 lbs. fibers/in.of width/hour. At these rates, the tufts which form at the fiberdeceleration zone, even though they are under favorable humidityconditions, are too large to form an acceptable quality product.

For this reason, the corona charging system was set up, to apply uniformelectrostatic charges to all fibers, immediately after they areseparated into small groups or individual fibers, so that they willsubsequently repel each other, and retain the initial good fiberopenness and distribution, until they are deposited on the condensingsurface.

The point where the fibers are charged must be after they have beendispersed into the gaseous medium, and is preferably immediatelyadjacent to the point of dis persion. This point is preferred because:(1) the fiber is at its best separated state, either fiber-by-fiber orin very small groups; (2) the fibers have just lost contact with thedisperser roll and are gas borne which means that they will retain thecharges transmitted to them, even though the relative humidity is high;(3) the fibers are close to an ideal target electrode at this pointsince the smaller the distance from the target, the more efficient isthe charging; (4) due to the good separation by the disperser, fibersfly along a single surface and there is essentially only one fiber inthe path between the ion emitting electrode and target electrode therebyassuring that the fibers are charged efficiently; and (5) the proximityof the fiber stream to the grounded target permits the use ofpractically any ion emitting electrode to target spacing desired to fitoptimum conditions as dictated by factors such as the disperser rollclothing, voltage levels permissible, polarity and stability desired,etc.

Commercially known air laydown nonwoven web forming machines can besuitably modified to provide the machines of this invention. Asmentioned above, the most commonly known machine is sold under the nameRando-Webber by Curlator Corp. The patents incorporated by referenceabove disclose many embodiments of the Rando-Webber which can bemodified to include a corona discharge system to uniformly charge thefibers subsequent to their distribution into a gaseous medium. Theincorporated references are also relied upon for their disclosure of webforming machines suitable for modifi cation according to the principlesof this invention.

Two relatively simple modifications which can be made to Rando-Webbersto provide them with a suitable corona discharge system are shown inFIGURES 1 and 2.

The first merely involves redesigning the removable saber tube 17 sothat it supports an ion emitting electrode 7 within a recessed area 18.If desired, the saber tube 17 can be partially or completely constructedof an electrical insulating material. When the ion emitting electrode 7is properly mounted in the saber tube 17, the tube is replaced in theRando-Webber and positioned so that the needle tips 12 of the electrode7 are located at a point where the fibers 5 have been dispersed into thegaseous medium 4, which in the case of a Rando-Webber is an air stream.To complete the corona discharge system, the disperser roll 3isconnected to ground and the ion emitting electrode 7 is connected to asource of electrical power. This is a particularly preferred embodimentof the invention because charging takes place very close to the pointwhere the fibers leave the disperser roll 3 and because the requiredmodifications to the saber tube 17 can be made quickly andinexpensively.

A second relatively simple modification can be. made to a Rando-Webberby cutting out a recessed area 18 in the machines interior housing 19 ata point close to where the fibers 5 leave the disperser roll 3 to becomeairborne and then mounting an ion emitting electrode 7 in the recessedarea 18. The disperser roll 3 can again be grounded and act as thetarget electrode.

As shown in FIGURES 1 and 2, a Rando-Webber can be modified to beequipped with two corona discharge systems, one being located in thesaber tube 17 and the other being located in the machines interiorhousing 19. Other locations are also possible. The advantage to multiplecorona discharge systems is that they can be turned on singly,simultaneously, consecutively,

in various combinations, or they can all be turned off. Their merepresence, aslong as the ion emitting electrode 7 is recessed, does notadversely affect web characteristics.

Fiber stock 1 is fed to the disperser roll 3 by feeding means which canbe simple or complex. Simple feeding means include a feed roll 2,conveyor, shute, etc. More complicated feeding means include mechanismssuch as Rando-Feeders, sold by the Curlator Corp. One typicalRand-Feeder is described in detail in Buresh et al., U.S. Patent2,744,294, issued May 3, 1956.

Apparatus for creating a corona discharge system is also well known inthe art. In general, an apparatus is used utilizing an electricallycharged ion emitting electrode 7, preferably negatively charged,.havingat least one and preferably more needle points 12 disposed in line andspaced apart from a cylindrical target electrode 9 which is grounded. Ashaped, intense electrical field is established between the electrodescontaining a region of high and substantially unipolar ion chargedensity in proximity to the surface of the target electrode 9 throughwhich region the dispersed gas borne fibers 5 are passed.

The corona discharge is believed to operate on the following principle.When an electric field is established between a negative point and sometarget or ground with an intervening air gap, generally in that air gapthere are many free ions due to the action of normal backgroundradiation. As the electric field intensity is increased, the freepositive ions move under the influence of the field and are acceleratedtoward the negative point electrode. Upon colliding with that electrode,the ion transfers sufiicient kinetic energy to the electrode to overcomethe surface work function and, as a result, several electrons areemitted from the electrode. The emitted electrons acquire kinetic energyfrom the field, and collide with atoms in theair. These collisions causefurther ionization and the process avalanches. Thus, near the point theelectron avalanches produce an ion space charge, and at some distancefrom the point, the field strength, becomes low enough for the electronsto attach to neutral atoms through electron sharing, and form negativeions which move under the influence of the field toward ground; Theprocess is regenerative and since charge carriers of both signs aregenerated, eventually the air gap zone stabilizes into three regions.Close to the negative point electrode there is a region which is termedbipolar flow. It contains positive ions moving toward the pointelectrode and a greater number of electrons moving in the direction ofthe ground. Farther away from the point electrode and beyond or in theregion of electron attachment there is a region which is termed that ofthe bipolar cloud, since it contains charge carriers of both signs andis made up of electrons and air atoms which, of course, are mainlynitrogen and oxygen which have either gained or lost an electron. Theregion between the cloud and the ground plane or target is termed theregion of unipolar flow. It is substantially comprised of negative ionsmoving toward the ground plane with perhaps very few electronscontributing to flow in this region.

Since a large number of fibers are to be charged, it is desirable to usean ion emitting electrode 7 with many needle points 12 spacedtransversely across the electrode base 11 as shown in FIGURE 5. Thespacing depends upon the amount of fibers to be charged and otherfactors. Preferably, the spacing is about every Me" to about every 4"across the electrode base 11.

The ion emitting electrode is connected to an electrical source ofpower. Direct current is preferable because there is a directrelationship between the current level and charge level, thereby makingit desirable to use a very constant amount of current. The power sourceshould be capable of supplying from about 5 to about kilovolts to theion-emitting electrode 7 and preferably should supply from about 10 toabout 50 kilovolts.

The amount of current required depends upon the number and spacing ofthe needle points 12 on the ion emitting electrode base 11. For a needlepoint spacing of Aa-Vz inch, an amount of current should be supplied bythe power source to provide a current at the needle points 12 of fromabout 1 to about 30 microamps and preferably from about 5 to about 2'0microamps. In any case, the charge imparted to the gas borne fibers 5should be from about 0.1 to about 10 microcoulombs per gram of fibersand is preferably from about 0.5 to about 5 microcoulombs per gram offibers. The preferred voltage, current and charge density ranges havebeen found to help insure that initial fiber distribution is maintaineduntil the fibers are condensed. Of course, the power source is connectedto the ion emitting electrode with electrical wiring.

Some examples of suitable power sources for this invention include: (1)Models DU-60 and 2040 manu factured by Spellman High Voltage Co., NewYork, N.Y.; (2) Model PSC-30-5-1 manufactured by Del ElectronicsCorporation, Mount Vernon, N.Y.; and (3) Model 230-6P manufactured bySorenson C0,, South. Norwalk, Conn.

For a more detailed description of corona discharge systems consideredsuitable for use with the present invention, see the following UnitedStates patents, all of which are herein incorporated by reference fortheir descriptions of such systems: Di Sabato et al., U.S. 3,163,753,issued Dec. 29, 1964; and Owens, U.S. 3,340,- 429, issued Sept. 5, 1967.

Any gaseous medium capable of being ionized is suitable for use withthis invention. Of course, each gaseous medium will have its ownionization characteristics, and accordingly, adjustments in physical andelectrical parameters will have to be made. Air is the preferred gaseousmedium because it is inexpensive, readily available and easily ionized.An air flow can be very simply provided by a fan system, as is used inRando-Webbers. When an air stream is used, the air velocity V, should befrom zero to about 30,000 feet per minute. A preferable air velocity Vis in the range of from about 1000 to about 10,000 ft. per minutebecause at such rates very uniform nonwoven webs can be formed.

Any type of fiber, natural or synthetic, can be used with the machine ofthis invention as long as it is capable of holding an electrical charge.Some examples of suitable fibers include: (1) %1 inch, 1 /2 denier perfilament (d.p.f.) viscose rayon staple; (2) 1 /22 inch, 1 /2 d.p.f.Dacron fiber with mechanical crimping; (3) %2 inch, 3 d.p.f. Dacronfiber with no crimping or with mechanical or spiral crimping; (4) %2inch, 3 d.p.f. nylon fiber with mechanical crimping; (5) /22 inch, 1 /2d.p.f. acetate fibers; and (6) a blend of 20-80% inch, 1 /2 d.p.f.acetate rayon, crimped or uncrimped, with 2080% 1-2 inch, 1 /2 d.p.f.Orion fiber, crimped or uncrimped. Dacron and Orion are registeredtrademarks of E. I. du Pont de Nemours & Co. for polyester and acrylicfibers, respectively.

The machine and process of this invention are useful for forming randomnonwoven web material from fibers. Nonwoven web material, in turn, hasmany of the same utilities of woven webs. In particular, nonwoven websare used to make fabrics for womens dresses, to make tent fabric, assubstrates for linoleum coverings, as substrates in fabric compositesand as interlinings on mens and womens suits and dresses. Nonwoven websare generally more economical than comparable woven web materials andoften can be made stronger per equivalent weight.

The following examples illustrate the invention. All parts andpercentages are by weight unless otherwise specified.

Examples 1-19 These examples were performed on a modified 40 inch wideRando-Webber type 40B. A model 40B type Rando- Feeder was used to feedthe web forming machine. Rando-Webber and Rando-Feeders are trade namesfor machines built and sold by Curlator Corp., East Rochester, NY.

The disperser roll was grounded and covered with garnett type cardclothing with 40 teeth/in. with a 66 in. tooth height. Normal operatingspeed of the roll was 2500 r.p.m. (9" roll size) or approximately 6,000surface feet per minute.

The air system of the Rando-Web'ber consists of dual blowers locatedinside the machine. Air from a plenum chamber, supplied by the outlet ofthe blowers, passes through a venturi formed by the saber tube and thelickerin cylinder. As the fibers are doffed, the air transports thefibers to the condensing roll where the web is formed. The air passesthrough the perforated condenser and returns to the inlet of theblowers. The air system is controlled by means of dampers located at theoutlets of the blowers.

The following modifications were made to the Rando- We'bber:

(1) Two corona ion emitting electrodes, each connected to a SpellmanModel DU-60 power source, were installed on the machine. One wasembedded in the saber tube and one was located in the lower plate of theair chamber. To eliminate fiber hangups on the grounded metal surface,the lower plate of the air duct and the metal dofi bar were changed toLucite. The saber tube was also changed to Delrin to accommodate thecorona electrode. Lucite and Delrin are trademarks of the E. I. du Pontde Nemours & Co. for acrylic resins and acetal resins, respectively;

(2) A minor modification was made to the duct shape to eliminate a lowpressure zone in the area of the feed device by inserting a smalltriangular piece of material to the interior housing of the machineimmediately above the saber tube.

The fibers used were one inch long rayon staple, sold by AmericanViscose. Approximate air velocity during these examples was 8500ft./min. at the saber tube venturi TABLE I Example No.

9 throat (V and 1000 t'L/min. in the condensation zone 2)- In an elfortto see the full effect of the charging system at rates with very low anddiflicult to achieve basis weights, web samples, usually of 1 oz./yd.nominal basis weight, were collected at different rates, usually 1, 1/2, 2%, 3 and 4 lbs./in. width/hour, at each machine setting, andvisually compared for blotchiness and relative uniformity to standardweb samples. Test results are given in Table I above.

Examples Nos. 1 and in Table I were made as a reference set with theunmodified Rando-Webber. Example No. l at 0.5 lb./in./hr. is identicalto the best of what is being produced presently by this machine.Uusually a quality between that of Example No. 1 and Example No. 2(between 0.5 and l lb./in./hr.) is acceptable. Consequently, any examplebetter than Example No. 2 was considered acceptable.

The 2 oz./yd. examples included in Table I were made to demonstrate therelative ease of producing 2 oz./yd. rather than'l oz./yd. examples.Blotches and basis weight nonuniformities tend to become masked. The webis also easier to handle.

Immediately over 1 lb./in./hr. (Examples 4 and over) quality drops belowthe acceptable limit. First blotches set in, and then gradually basisweight nonuniformities become more pronounced. Finally over 2.5.lb./in./hr., fiber chunks from the feed start escaping into the web, andthe product becomes totally unacceptable.

Examples 11 through 19 in Table I were made under identical conditionsas those of Examples 1-10, but with the electrostatic modifications. Inthis particular experiment both Corona wands were kept active, sincethis appeared to be slightly better than activating either wand byitself. The voltage-amperage settings used here were chosen for optimumperformance.

As shown in Table I electrostatics raised the productivity to the rangebetween 1.0 and 1.5 lb./in./hr. EX- ample made at 2 1bs./in./hr., isstill better than Example 2 made at 1 lb./ in./ hr. by the unmodifiedmachine, but not as good as Example 1 made at 0.5 lb./in./hr.

Examples 20-41 These examples were carried out on a 40 inch wideRando-Webber with a 5 /2 feet long by 40 inch wide Lucite duct and dualscreen condenser. Lucite is a registered trademark of E. I. du Pont deNemours & Co. for acrylic resins. The ion emitting electrode was mountedin a Delrin housing section to ensure that the shortest path to groundwas via the disperser roll. The Delrin section was mounted at a point inthe duct immediately below the saber tube. Delrin is a registeredtrademark of E. I. du Pont de Nemours & Co. for acetal resins. The ionemitting electrode was positioned so that the shortest path to groundwas to the disperser roll at a point where virtually all of the fiberwas airborne. A Del Electronics Model PSC-30-5-1 high voltage DC powersupply was connected to the ion emititng electrode. For these examples,Dacron polyester fiber of 1.85 and 2.75 d.p.f., 1.5 inches long. Dacronis also a registered trademark of E. I. du Pont de Nemours & Company forpolyester fiber.

The operating conditions were:

Feed condenser vacuum 0.8-1.1" of H 0.

Feed roll speed 15.8-20.7 ft./ min.

Lickerin roll speed 1900-2800 rpm. (9'' dia.). Air flow 2000-2700 c.f.m.

Relative humidity 45-70% at 70-80 F.

Batt weight 15-25 oz./yd.

Fiber flow rate 2-2.5 lb./in./hr.

Test parameters for these examples are given in Table 2.

TABLE 2 Corona Duct RH. Lickerin Milliper- Roll,

Kv. amps cent r.p.m. DPF

Example Example 40 41 Batt weight, or../yd. 15-16 24. 7 Fiber flow rate,lbs./in./hr 2 3 Chevron length, no charge, inche 3 4% Chevron length,with charge, inches. 6 6% Several eifects were visible with the coronasystem in use as compared to runs without use of the corona system. Thechevron changed dramatically in that it became much longer and sharper.The amount of fiber movement on the screens and the amount of barescreen were both visibly reduced. No fiber hangup on the duct or machineparts was observed.

Chevron length was marked by the insertion of black fiber at the feedroll and increased by as much as from 3 to 6". This increase was lessdramatic at high air flow rates but was at least 20% under allconditions. In all cases, the chevron became sharper going from U shapedor a short v shape to a longer, more pronounced V shape.

In all cases, fiber does move as it deposits on the bare screen or onother fibers; however, the amount of movement was visibly reduced whenelectrostatic charging was used. There also was visible evidence of anattraction of the fiber to the bare screen. With electrostatic charging,the fibers deposited closer to the leading edge of the dual condenserscreens.

The insertion of black fiber to define the chevron length also revealedthat the transverse direction and graded density distribution of theblack fiber were more uniform with electrostatic charging than without.

These effects were reproducible and observable for the ranges of fiberflow rates, batt weights, air flows, lickerin roll speeds, relativehumidities and fiber deniers previously listed.

Both positive and negative charging were efiective. However, thenegative charging is, in general, more stable and, therefore, preferred.The current and voltage levels did not seem to have much effect oncethey were above certain minimum levels. Typical effective operatingconditions for the 37" long charging electrode were -30 to 40 kv. at 1to 2. milliamps.

What is claimed is:

1. A machine for forming random fiber nonwoven webs by dispersing fibersin a gaseous medium and subsequently condensing said fibers onto aforaminous surface, comprising, in combination:

(a) means including a disperser roll for dispersing said fibers in saidgaseous medium;

(b) means for supplying said gaseous medium;

(0) means for feeding said fibers to said dispersing means;

(d) means for condensing said fibers from the gaseous medium;

(e) a duct connecting the dispersing means to the condensing means, saidduct containing the gaseous medium; and

(f) a corona discharge system located at a point beyond where the fibersare dispersed into the gaseous medium said corona discharge systemcomprising, in combination,

(1) an ion emitting electrode comprised of a plurality of conductingneedles fixed rigidly in a lateral spacial relationship arrangedtransverse to and completely across said fiber path with the points ofthe said needles facing said target electrode;

(2) a target electrode oppositely positioned across the path of thefibers in the gaseous medium said target electrode comprising saiddisperser roll and being connected to ground;

(3) a source of electrical current and voltage sufiicient to provide acorona vdischarge from said ion emitting electrode; and (4) meansconnecting said ion emitting electrode to the source of electricalcurrent and voltage. 2. A machine of claim 1 wherein said gaseous mediumcomprises an air stream flowing in the duct from the disperser roll tothe condensing means.

3. A machine of claim 2 wherein the means for feed- =ing said fibers tothe dispersing roll comprises at least one feed roll.

4. A machine of claim 3 wherein said means for condensing said dispersedfibers comprises a foraminous condenser roll.

5. A machine of claim 3 wherein said means for condensing said dispersedfibers comprises at least one foraminous conveyor belt.

6. A machine of claim 3 wherein said means for condensing said dispersedfibers comprises two foraminous conveyor belts angularly arranged in aconverging configuation.

References Cited UNITED STATES PATENTS 2,462,487 2/1949 Griffith et al19-144 2,810,426 10/1957 Till et a1. 188 XR 3,319,309 5/1967 Owens19-155 XR DORSEY NEWTON, Primary Examiner

